The invention relates to a shaving head provided with a cutting member which has a cutting edge for cutting hairs which grow from skin, and with a hair manipulator which is arranged in front of the cutting edge, as seen in a shaving direction of the shaving head, and which can be driven in a direction substantially parallel to the cutting edge for moving the hairs in a direction substantially parallel to the cutting edge.
The invention also relates to an electric shaver provided with a shaving head and a drive unit, in which the shaving head is provided with a cutting member which has a cutting edge for cutting hairs growing from skin, and with a hair manipulator which is arranged in front of the cutting edge, as seen in a shaving direction of the shaving head, and which can be driven by means of the drive unit in a direction substantially parallel to the cutting edge for moving the hairs in a direction substantially parallel to the cutting edge.
A shaving head and an electric shaver of the kinds mentioned in the opening paragraphs are known from EP-B-0 855 256. The cutting member of the known shaving head and the known electric shaver comprises a straight cutting edge which extends perpendicularly to the shaving direction and is arranged in a fixed position in the shaving head. The hair manipulator comprises a comb which is arranged parallel to the cutting edge with teeth which extend substantially perpendicularly to the cutting edge. Reciprocal displacements of the hair manipulator relative to the cutting member are generated in a direction parallel to the cutting edge by means of the drive unit during operation. When a user moves the shaving head in the shaving direction over the skin, the hairs are first caught between the teeth of the hair manipulator. The teeth have comparatively small interspacings, so that reciprocal movements of the hairs in a direction substantially parallel to the cutting edge are generated by the hair manipulator, and the hairs are moved to and fro along the cutting edge during cutting. The result of this is that a required cutting force in the shaving direction for cutting through the hairs is considerably reduced, whereby the shaving performance and the shaving comfort offered by the shaving head are considerably improved. The hair manipulator also offers the skin a protection against skin damage and skin irritation. As a result of the displacement of the shaving head in the shaving direction over the skin, the skin is stretched immediately in front of the cutting edge in a direction parallel to the shaving direction by means of the teeth of the hair manipulator, so that comparatively large skin folds in front of the cutting edge, which could cause skin cuts, are largely prevented. As a result of said reciprocal movements of the hair manipulator, in front of the cutting edge the skin is also stretched parallel to the cutting edge, so that also comparatively small skin folds between the teeth of the hair manipulator, which could cause minor skin damage or skin irritation, are largely prevented.
It is a disadvantage of the known shaving head and the known electric shaver that the hair manipulator used therein does not completely prevent skin cuts and skin irritation. This is because there is only a limited frictional force present between the hair manipulator and the skin, with the result that the hair manipulator glides over the skin for the major part during said reciprocal displacements. The hair manipulator thus stretches the skin parallel to the cutting edge to a limited degree only, so that skin folds in front of the cutting edge are not completely prevented.
It is an object of the invention to provide a shaving head and an electric shaver of the kinds mentioned in the opening paragraphs with which the skin immediately in front of the cutting edge is better stretched, so that the disadvantage of the known shaving head and the known electric shaver mentioned above is obviated as much as possible.
To achieve this object, a shaving head according to the invention is characterized in that the cutting member can be driven in a direction parallel to the cutting edge such that the cutting member and the hair manipulator move in opposite directions for longer periods than in equal directions, as seen parallel to the cutting edge, during operation.
To achieve this object, an electric shaver according to the invention is characterized in that the shaving head used therein is a shaving head according to the invention.
Since the cutting member can be driven in a direction parallel to the cutting edge, a frictional force directed parallel to the cutting edge is present between the cutting member and the skin as a result of displacements of the cutting member relative to the skin in said direction. The result is that the skin lying immediately in front of the cutting edge is stretched in a direction parallel to the cutting edge not only by the hair manipulator, but also by the cutting member. Since the cutting member and the hair manipulator move in opposite directions, as seen parallel to the cutting edge, for longer periods than in equal directions during operation, the frictional forces exerted by the cutting member and the hair manipulator on the skin present directly in front of the cutting edge have opposite directions more often than equal directions over a predetermined period of time. Since the points of application of the frictional forces of the cutting member and of the hair manipulator on the skin lie at a distance from one another, a shearing stress present in the skin lying immediately in front of the cutting edge as a result of the frictional force of the hair manipulator is increased by the frictional force of the cutting member, when averaged over said period of time. The cutting member thus reinforces the stretching action performed by the hair manipulator on the skin present immediately in front of the cutting edge, so that skin folds immediately in front of the cutting edge are further limited, and skin cuts and skin irritation are prevented to a greater extent. An additional advantage is that the hairs are displaced relative to the cutting edge with a higher velocity, seen parallel to the cutting edge and averaged over a predetermined period of time, during cutting, so that the cutting force required in the cutting direction for cutting the hairs is further reduced. Since the hair manipulator and the cutting member can both be driven in a direction parallel to the cutting edge, i.e. in a direction perpendicular to the shaving direction, a frictional force present between the hair manipulator and the skin and a frictional force present between the cutting member and the skin have only comparatively small components in a direction parallel to the shaving direction, so that the user only experiences a comparatively small frictional force in the displacement of the shaving head in the shaving direction over the skin. The shaving comfort is further enhanced thereby.
A special embodiment of a shaving head according to the invention is characterized in that the cutting member and the hair manipulator can be driven into oscillatory movements having the same frequency and a mutual phase difference of between 90xc2x0 and 270xc2x0, as seen parallel to the cutting edge. If the cutting member and the hair manipulator perform oscillatory movements with a mutual phase difference of between 90xc2x0 and 270xc2x0, the cutting member and the hair manipulator will move more often in opposite directions than in equal directions parallel to the cutting edge, seen over one cycle of the oscillatory movement, so that the mutually reinforcing stretching actions of the hair manipulator and the cutting member on the skin present immediately in front of the cutting edge are provided by means of movements of the hair manipulator and the cutting member which can be realized in a simple manner.
A further embodiment of a shaving head according to the invention is characterized in that said phase difference is substantially equal to 180xc2x0. If the cutting member and the hair manipulator perform oscillatory movements in a direction parallel to the cutting edge with a mutual phase difference of 180xc2x0, the cutting member and the hair manipulator will move continuously in mutually opposed directions, so that the mutually reinforcing stretching actions of the hair manipulator and the cutting member on the skin present immediately in front of the cutting edge are a maximum. The fact that the cutting member and the hair manipulator continuously move in mutually opposed directions means that mass forces exerted by the cutting member and the hair manipulator on the shaving head as a result of the oscillatory movements compensate each other, provided the values of the displaceable masses of the cutting member and the hair manipulator are suitably chosen, so that the shaving head is substantially free from vibrations.
A yet further embodiment of a shaving head according to the invention is characterized in that the phase difference is approximately 135xc2x0 or approximately 225xc2x0. This yet further embodiment not only achieves a considerable enhancement of the mutually reinforcing stretching actions of the hair manipulator and the cutting member on the skin present immediately in front of the cutting edge, but it also provides a considerable probability of a temporary clamping of the hairs between the hair manipulator and the cutting member. Such a temporary clamping has the result that hairs are first pulled from the skin over some distance before the hairs are cut through by the cutting member. An achievable skin smoothness is considerably increased thereby.